Question

Looking through the jQuery source in the function now() I see the following:

function now(){
    return +new Date;
}

I’ve never seen the plus operator prepended to the new operator like this. What does it do?

Answer 1

Nicolás and Brian are right, but if you’re curious about how it works, +new Date(); is equivalent to (new Date()).valueOf();, because the unary + operator gets the value of its operand expression, and then converts it ToNumber.

You could add a valueOf method on any object and use the unary + operator to return a numeric representation of your object, e.g.:

var productX = {
  valueOf : function () {
    return 500; // some "meaningful" number
  }
};

var cost = +productX; // 500